Drug self-administration, like other learned behaviors, is acquired, maintained and can be extinguished and reinitiated. Environmental (e.g., schedule of reinforcement), pharmacological (e.g., drug dose) and organismal variables can influence drug-maintained behaviors. The purpose of the research in the present proposal is to use an animal model of drug abuse to investigate how environmental and pharmacological variables can affect maintenance and reinitiation of drug taking as well as behaviors generated by schedules of drug self-administration. Three series of experiments are proposed. The purpose of the first series is to examine the effect of manipulating several environmental variables on drug self-administration. Monkeys will be trained in a discrete-trials choice procedure to choose between a drug injection and a non-drug reinforcer, food. The effect of environmental variables such as schedule of reinforcement and punishment on the frequency of drug choice will be determined. The purpose of the second series is to examine variables that influence the probability that extinguished drug self-administration will be reinstated. Monkeys will be allowed to self-administer drug or saline and the ability of pre-session drug injections to reinstate responding for saline will serve as a model for relapse. The effect by environmental (e.g., schedule of reinforcement) and pharmacological (e.g., drug that maintains behavior) on the probability that a drug injection will reinstate the self-administration response will be examined. The third series is designed to pursue the finding that certain schedules of drug self-administration can generate excessive behavior that is not directly related to the drug injection. It is likely that the behavior can be classified as an adjunctive behavior. Experiments are proposed that will further examine the similarities between this and other adjunctive behaviors by examining conditions of drug availability that generate excessive behavior. In addition, modification of the behavior by environmental and pharmacological consequences will be examined. Taken together, these experiments will expand our knowledge of the variables that control acquisition, maintenance and reinitiation of drug self-administration. In addition, we will begin to explore other behavioral concomitants of drug self-administration. The results will have important implications for our understanding of the variables that control, as well as the behavioral complexity of, drug abuse in humans.